1. Field of the Invention
Aspects of the present invention relate to an image forming apparatus, and more particularly, to an image forming apparatus capable of reducing a temperature difference of a photosensitive body.
2. Description of the Related Art
An image forming apparatus forms a predetermined image on a printing medium and may be generally classified as one of an inkjet type and an electrophotographic type according to the method by which the image forming apparatus forms images. The electrophotographic image forming apparatus generally forms an image through charging, exposing, developing, transferring, cleaning, and discharging operations. The electrophotographic image forming apparatus includes a photocopier, a laser printer, and the like.
As shown in FIG. 1, a conventional electrophotograhic image forming apparatus 1 includes a photosensitive body 5; a photosensitive body frame 4, which rotatably supports a rotation shaft 5a of the photosensitive body 5; and a driver 2 which rotatably drives the photosensitive body 5. A first end part of the rotation shaft 5a of the photosensitive body 5 is connected with a photosensitive body driving gear 5b. An electrostatic latent image is formed on the photosensitive body 5 corresponding to image information. The formed image is developed with a toner by a developing cartridge (not shown). A remaining toner on the surface of the photosensitive body 5 is stored in a scrapped toner container 6 after the formed image transfers to a print paper.
The driver 2 is supported by a supporting bracket 3. A rotation shaft 2a of the driver 2 is connected with a driving pinion 2b. The driving pinion 2b is engaged with a first gear train of a transmission gear 7. The photosensitive body driving gear 5b is engaged with a second gear train of the transmission gear 7 to transmit driving force of the driver 2 to the photosensitive body 5.
The supporting bracket 3 includes a metal material, and heat generated from the driver 2 is conducted directly to the supporting bracket 3. Thus, significant difference in surface temperature is produced between the two sides of the photosensitive body 5 as the side of the photosensitive body 5 nearest the driver 2 is heated by the heat generated by driver 2.
Temperatures at seven points, from point A to point G, were measured after operating the conventional image forming apparatus 1 for six consecutive hours resulting in the following Table 1. An initial temperature of the respective points was 23.5° C. The temperatures of the points A and G correspond to those of the photosensitive body frame 4. The temperatures of the points B to F refer to surface temperatures of the photosensitive body 5.
TABLE 1PointABCDEFGTemp.58.7° C.55.6° C.54.9° C.54.5° C.54.3° C.53.0° C.49.6° C.
If the surface temperature of the photosensitive body 5 rises, a residual surface potential of the photosensitive body 5 rises by approximately 50V to thereby reduce a potential difference between a developing roller (not shown) of the developing cartridge. The reduced potential difference decreases the amount of the toner moving to the photosensitive body 5 from the developing roller to thereby lower a density of an image.
As shown in Table 1, a maximum surface temperature difference of approximately 3° C. occurs between points B and F of the photosensitive body 5, thereby causing the density of the image formed at points B and F to be different.
Other than the temperature difference of the photosensitive body 5, temperature difference also occurs in the developing cartridge disposed adjacently to the photosensitive body 5, which develops the photosensitive body 5 with the toner. Thus, flow properties of the toner stored in the developing cartridges (not shown) are changed to thereby further decrease quality of the image.
If a forced cooling means, such as a cooling fan (not shown), is used, it becomes difficult to manufacture a light and small image forming apparatus. As such, it is necessary to find a different solution to address the temperature difference between the two ends of the photo sensitive body 5.